Paper sheet identifying and checking apparatus

ABSTRACT

In a paper sheet identifying and checking apparatus including a conveying path to convey a bill, a line sensor including a plurality of light sensor elements arranged on the conveying path in a string in a conveying width direction, and an identifying module to identify the paper sheet on the basis of a binary image produced by the line sensor by reading the paper sheet, the direction of arranging the sensor elements is inclined with respect to the conveying width direction of the conveying path.

INCORPORATION BY REFERENCE

The present application claims priority from Japanese applicationJP2006-154863 filed on Jun. 2, 2006, the content of which is herebyincorporated by reference into this application.

BACKGROUND OF THE INVENTION

The present invention relates to a paper sheet identifying and checkingapparatus for identifying a paper sheet, for example, a paper money(banknote) or a bill conveyed thereto, and in particular, to a papersheet identifying and checking apparatus for producing image data of apaper sheet by use of an optical line sensor and identifying a kind andtruth or falsehood of the paper sheet on the basis of the image data.

Heretofore, the bill identifying and checking device of the prior artincludes an optical sensor to detect a position of a passage of a papersheet and gradient or inclination thereof relative to a direction toconvey the paper sheet. The bill identifying and checking device detectsthe position of the passage of the paper sheet on the basis of timing ofa change in an output from the optical sensor and detects the gradientof the paper sheet on the basis of a difference in time between changesin outputs from sensor elements that is generated due to the gradient ofthe paper sheet.

JP-A-8-212417 describes a device conducting the detection in which anoptical line sensor almost entirely covering the width of the conveyingpath is installed in a direction vertical to the conveying direction inwhich a paper sheet is conveyed in the conveying path. The deviceincludes a rotary encoder to generate a conveyance pulse at a fixedperiod each time the paper sheet is slightly conveyed, a frame memory tobinarize the output from the optical line sensor at timing synchronizedwith the conveyance pulse and to store therein the binary valueresultant from the binarization, and an image processing module todigitalize the data stored in the frame memory. In the device, theconveying path is scanned in a direction perpendicular to the conveyancedirection at timing synchronized with the conveyance pulse to therebystore a two-dimensional binary image of the paper sheet in the framememory. For example, if the optical line sensor includes opticalelements at a pitch or interval of one millimeter (mm) and the rotaryencoder generates one pulse each time the paper sheet is conveyed onemillimeter, there is obtained a binary image having a contour of a 1 mmby 1 mm square. The device execute image processing for the binary imageto resultantly calculate the position and the gradient of each edge ofthe paper sheet.

SUMMARY OF THE INVENTION

However, in the device of this type, if the gradient of the paper sheetbeing conveyed is almost zero, precision in the detection of theposition and the gradient of the paper sheet is lowered due to influenceof a quantization error. For example, in a situation wherein theconveyance pulse has a period of one millimeter, if the gradient of thepaper sheet is less than one millimeter, the edges of the paper sheetare seen as if there is no gradient in the obtained image relative tothe direction vertical to the conveying direction. In this case, thereis obtained one and the same result regardless of the position of thepaper sheet between the conveyance pulses, leading to a maximum error of0.5 mm.

Particularly, in the bill identifying and checking device to identify abill, it is quite important to detect the slight difference between atrue or authorized bill and the false or counterfeit bill without fail.Therefore, it is desirable to possibly prevent the deterioration in theidentifying performance due to the error described above.

To improve the identifying performance, there may be employed a methodin which the scanning frequency is increased by shortening the period ofconveyance pulses. In this method, the detection precision is improvedin the conveying direction regardless of the magnitude of the gradientof the paper sheet; moreover, the detection precision is also improvedwhen the gradient is almost zero. For example, when a rotary encoderhaving a conveyance pulse period of 0.5 mm is used, the detectionprecision in the conveying direction is twice that when a rotary encoderhaving a conveyance pulse period of 1 mm is used. However, as comparedwith the case using a rotary encoder having a conveyance pulse period of1 mm, there are required a higher-speed optical line sensor, alarger-capacity frame memory, and a higher-performance image processingmodule. Therefore, the cost of the bill identifying and checking devicesoars.

It is therefore an object of the present invention to provide a papersheet identifying and checking apparatus wherein even when the gradientof the paper sheet relative to the direction vertical to the conveyancedirection is almost zero, the gradient of the paper sheet can bedetected with precision less than the period of conveyance pulses whilekeeping the cost of the device unchanged.

According to an aspect of the present invention, there is provided apaper sheet identifying and checking apparatus including a conveyingpath for conveying a paper sheet, a line sensor including a plurality ofsensor elements arranged on the conveying path in a string in aconveying width direction indicating a direction of width of theconveying path, and an identifying module for identifying the papersheet on the basis of image data produced by the line sensor by readingthe paper sheet. The direction of arranging the sensor elements isinclined with respect to the conveying width direction of the conveyingpath.

Other objects, features and advantages of the invention will becomeapparent from the following description of the embodiments of theinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a bill identifying and checkingapparatus;

FIG. 2 is a plan view of a lower unit of the bill identifying andchecking apparatus;

FIG. 3 is a block diagram showing structure of the bill identifying andchecking apparatus;

FIG. 4 is a diagram for explaining image data in a frame memory;

FIG. 5A is a diagram for explaining a quantization error;

FIG. 5B is a diagram for explaining a quantization error; and

FIG. 6 is a graph showing a frequency distribution of the short-edgelength of a bill in the conveying direction.

DESCRIPTION OF THE EMBODIMENTS

Referring now to the drawings, description will be given of anembodiment of the present invention.

The embodiment relates to a bill identifying and checking apparatus forconveying a bill as a paper sheet and identifying the bill. “Identifyingthe bill” indicates to determine the kind of bill, for example, a newthousand-yen bill, an old thousand-yen bill, or a two-thousand-yen billin Japan and to determine whether the bill is an authorized bill or acounterfeit bill. The term “bill” implies the authorized and counterfeitbills. The bill identifying and checking apparatus is incorporated in,for example, an Automatic Teller's Machine (ATM) of a financial sectionof a bank to identify bills.

First, an outline of the bill identifying and checking apparatus will bedescribed by referring to the perspective view of the bill identifyingand checking apparatus 1 shown in FIG. 1 and the plan view of the lowerunit 4 of the apparatus 1 shown in FIG. 2.

The bill identifying and checking apparatus 1 includes an upper unit 2and a lower unit 4 installed respectively on the upper and lower sidesof a conveying path 3. On an upper surface of the lower unit 4, a lightprojector section 23 a of an optical line sensor 23 is arranged toalmost entirely cover the width of a conveying width L, the projectorsection 23 a being inclined by an angle of θ from the conveyingdirection (the vertical direction in FIG. 2) to the conveyance widthdirection (the horizontal direction in FIG. 2).

The conveyance width direction indicates a direction vertical to theconveying direction. By inclining the line sensor 23 by an angle of θrelative to the conveyance width direction, it is possible that the billpasses the line sensor 23 in an inclined state in which the bill isinclined with respect to the line sensor 23.

On the upper surface of the lower unit 4, a plurality of conveyingrollers 22 are disposed to convey the bill and various sensors 21 otherthan the line sensor 23. On a lower surface of the upper unit 2, thereis disposed a light receiver section, not shown, of the optical linesensor 23 to oppose the projector section 23 a in the verticaldirection. Therefore, like the projector section 23 a, the lightreceiver section is also disposed in an inclined state with an angle ofθ as described above.

The conveying path is a path in which the bill 6 is conveyed in adirection indicated by an arrow A.

The lower unit 4 is connected to various devices arranged in the ATM.

A gear 5 links a motor in the ATM with the conveying rollers 22 of thebill identifying and checking apparatus 1 to rotate the rollers 22 bydriving force of the motor.

Various sensors 21 input and output signals such as waveforms accordingto purposes thereof.

The rollers 22 are rollers which rotate the bill 6 sandwichedtherebetween. The rollers 22 are linked via the gear 5 with the motor ofthe ATM to convey the bill 6 at a fixed conveying speed.

The optical line sensor 23 reads an image of an optical pattern.

FIG. 3 shows structure of the bill identifying and checking apparatus 1in a block diagram.

The bill identifying and checking apparatus 1 includes conveying rollers22, a rotary encoder 31, an optical line sensor 23, an optical linesensor driver 32, a frame memory 33, an image processing module 34 toprocess images, and an identifying module 35 to identify a bill.

The conveying rollers 22 are disposed to convey the bill 6 sandwichedtherebetween in the conveying direction. Four axes are disposed in thedirection vertical to the conveying direction indicated by an arrow andfour rollers are attached to each axis. Each conveying roller 22 islinked via the gear 5 with the motor of the ATM to convey the bill 6 ata fixed conveying speed.

The rotary encoder 31 is attached to one of the rotary axes of theconveying rollers 22 or to one of the conveying rollers 22 to generate aconveyance pulse at a fixed period each time the bill 6 is slightlyconveyed.

The optical line sensor 23 includes a plurality of light projectorelements arranged on the light projector section 23 a in a line with anequal interval therebetween and a light receiver element array includinga plurality of light sensor elements on the light receiver section in astring or line with an equal interval therebetween. The light projectorelements and the light receiver element array are disposed with theconveying path 3 therebetween in a symmetric way along the verticaldirection. The light projector section 23 a and the light receiversection are disposed with an inclination angle of θ relative to thedirection vertical to the conveying direction, while they aresubstantially in parallel with each other in a plane including the lightprojector section 23 a and the light receiver section. The line sensor23 thus configured covers almost the entire width of the conveying path3 and hence serves a function to capture a one-dimensional image of theconveying path through one image sensing operation. In general, the linesensor 23 is arranged in a direction vertical to the conveyingdirection. However, according to the present invention, the line sensor23 is inclined by the inclination angle θ. The angle θ is larger than askew allowance angle indicating allowance for the skew or inclination ofthe bill 6 conveyed through the conveying path 3.

The optical line sensor driver 32 has a function to binarize the outputfrom the line sensor 23 at timing synchronized with the conveyance pulseof the rotary encoder 31 and to write the binary data in the framememory 33. The driver 32 sequentially writes the one-dimensional binarydata in the frame memory 33 to resultantly produces a two-dimensionalbinary image therein. The binary image is image data of an opticalpattern of substantially the overall surface of the bill.

The frame memory 33 has a function to hold therein the two-dimensionalbinary image of the bill for a fixed period of time. The frame memory 33keeps the binary image stored therein while the image processing module342 executes its processing.

The image processing module 34 has a function to read the binary imageof the bill from the frame memory 33 to calculate (estimate) a positionand a gradient (angle of inclination) of each edge of the bill. Tocalculate the gradient of the bill, the processing module 34 serves as agradient calculation unit. To calculate the position of the edge of thebill, the processing module 34 serves as an outer contour detectingunit. The positions and gradients of four edges of the bill calculatedby the processing module 34 are fed to the identifying module 35disposed in a subsequent to the processing module 34.

Based on the positions and gradients of four edges of the bill, theidentifying module 35 determines the kind of the bill 6 and whether thebill 6 is an authorized bill or a counterfeit bill to thereby identifythe bill 6.

To determine positions of the edges of the bill, the bill identifyingand checking apparatus 1 thus constructed conducts operation as below.

First, when the motor of the ATM, not shown, rotates the conveyingrollers 22, the rollers 22 convey the bill 6. The rotary encoder 31attached to one of the axes of the conveying rollers 22 generatesconveyance pulses. At timing of the conveyance pulses, the line sensordriver 32 binarizes the output from the line sensor 23 to produce binarydata and then writes the binary data in the frame memory 33. Theone-dimensional binary data is sequentially written in the frame memory33. As a result, a two-dimensional binary image B (image data) of thebill 6 is generated in the frame memory 33 as shown in the explanatorydiagram of image data of FIG. 4.

The image processing module 34 reads the binary image B of the bill 6from the frame memory 33 to calculate the positions of four edges of thebill. Assume in the calculation that the physical coordinate value inthe conveyance direction is represented by Y′ and that in the conveyingwidth direction vertical to the conveyance direction is represented byX′. For a straight line y′=ax′+b in the space of coordinates (X′,Y′),coefficients a and b are obtained for the four edges of the bill 6.Specifically, from the binary data items obtained for each edge, thesystem selects the outer-most string of points and then replaces thestring of points by data items in the space of coordinates (X′,Y′). Thevalues of the coefficients a and b are obtained by applying the methodof least squares to the data items. As above, the analog data isconverted into digital data, and then an appropriate calculation isconducted by use of the digital data to thereby obtain the positions ofthe edges of the bill.

On the other hand, since the line sensor 23 is inclined as describedabove, the binary image B in the frame memory 33 appears as a correctrectangle on an image inclined by an angle of θ as shown in FIG. 4. Ifthe frame memory coordinates are represented as (X,Y), the physicalcoordinates (X′,Y′) are obtained through coordinate transformation usinga determinant of expression (1) as below. $\begin{matrix}{\begin{pmatrix}x^{\prime} \\y^{\prime}\end{pmatrix} = {\begin{pmatrix}1 & 0 \\{\sin\quad\theta} & 1\end{pmatrix}\begin{pmatrix}x \\y\end{pmatrix}}} & (1)\end{matrix}$

The unit can also be converted by multiplying the right side ofexpression (1) by “unit of physical coordinates/unit of frame memorycoordinates”.

Next, description will be given of a relationship between the billidentifying and checking operation by the identifying module 35 and thepositions of the edges of the bill. In the operation to identify thebill 6 by the sensors 21 including the optical line sensor 23, if thereexists a particular section of the bill 6, a relative position of theparticular section is beforehand determined relative to a particularposition such as a center or an angle of the bill 6. The particularsection of the bill 6 is then identified on the basis of the positionsof the edges of the bill 6 actually passed through the conveying path 3and the beforehand determined relative position. For the identifiedsection, the line sensor 23 and the sensors 21 process features of thesection to resultantly identify the bill 6. That is, precision of thepositions of the edges of the bill directly affects precision of theposition of the section of the bill 6 to be identified. In the operationto identify the bill 6 on the basis of the particular section, theprecision of the position of the section of the bill 6 greatly exertsinfluence upon precision to identify the bill 6.

According to the embodiment, as can be seen from FIG. 4, the lower-leftcorner 6 a of the bill 6 is in column 6 of conveyance pulses P of thebill 6 and the lower-right corner 6 b thereof is in column 2 ofconveyance pulses P. That is, these corners are read at different pointsof timing of conveyance pulses. Therefore, the straight line (the loweredge of the bill 6) between the lower-left corner 6 a and thelower-right corner 6 b exists in the frame memory 33 in association witha plurality of conveyance pulses P. It is hence possible to prevent anevent in which the lower-left corner 6 a and the lower-right corner 6 bexist on one and the same conveyance pulse P. Therefore, the position ofthe bill 6 can be detected with higher precision by reducing thequantization error.

Description will now be given of the quantization error appearing whenthe bill 6 is not inclined relative to the line sensor 23 shown in FIG.5A and that occurring when the bill 6 is inclined relative to the linesensor 23 shown in FIG. 5B. Since the line sensor 23 is arranged in aninclined state according to the embodiment, the image is actuallyinclined as shown in FIG. 4. However, for easy understanding ofexplanation, description will be given of a case in which the linesensor 23 is disposed without inclination with respect to the conveyingdirection

Each pixel 40 is defined on the basis of the period of conveying pulsesand the pitch of or the interval between optical elements of the linesensor 2. An outer contour of analog image 41 is an actual outer contourof the bill 6, and a digital image 42 is an area for the bill 6recognizable in digital processing. An outer contour of digital image 43is an outer contour of the bill 6 obtain by use of the digital image 42.

If the bill 6 is conveyed in a state of FIG. 5A without inclining thebill 6 relative to the line sensor 23, the position of the bill 6 isidentified at precision equal to or less than one pixel 40 determined bythe period of conveying pulses and the interval between opticalelements. This leads to a large error in the operation to identify thepositions of the edges of the bill 6. On the other hand, if the bill 6is conveyed in a state of FIG. 5A by inclining the bill 6 relative tothe line sensor 23, the edges of the binary image B appear in the formof steps. By drawing a regression line (obtainable using the method ofleast squares) for the associated pixels 40, the positions of the edgesof the bill 6 can be identified at higher precision. For example, bydrawing straight lines for ten pixels in a direction vertical to onestep in the conveying direction, the precision in the conveyingdirection is ten times that of one pixel.

Description will now be given of the improvement of the precision. FIG.6 is a graph showing a frequency distribution of the short-edge lengthof the bill 6 (in the conveying direction) in the bill identifying andchecking apparatus 1 including the optical line sensor 23 attached in adirection vertical to the conveying direction. Specifically, FIG. 6shows the frequency distribution when the bill 6 is inclined relative tothe line sensor 23 with an inclination angle equal to or less than onedegree and the frequency distribution when the bill 6 is inclinedrelative to the line sensor 23 with an inclination angle more than onedegree. As can be seen from FIG. 6, when the gradient is large (equal toor more than one degree), the frequency distribution of the short-edgelength is represented with a gentle slope centered on the mean value.However, when the gradient is small (less than one degree), thefrequency distribution of the short-edge length includes two peaks. Thatis, the larger the gradient is, the higher the precision in theshort-edge is. According to the present invention, the optical linesensor 23 is beforehand disposed in the inclined state, and hence it issecured that the bill 6 is inclined with respect to the line sensor 23to thereby improve the precision to determine the position of the bill6.

By disposing the line sensor 23 in the inclined state as above, theposition and the gradient of the paper sheet can be detected in theconveying direction with high precision regardless of the magnitude ofthe inclination of the paper sheet. It is therefore possible to providethe bill identifying and checking apparatus 1 with higher identifyingprecision.

Since the line sensor 23 is inclined such that the angle of inclinationthereof exceeds the skew allowance range of the bill identifying andchecking apparatus 1, the binary image B can be produced such that thefront edge and the rear edge of the paper sheet are represented in theshape of steps regardless of how the paper sheet, i.e., the bill 6 isskewed or inclined.

As a result, it is guaranteed that a step-wise image of the bill 6 isproduced and the position and the gradient of the bill 6 are detected inthe conveying direction with precision less than the conveying pulse. Incomparison with the case in which the line sensor 23 is attached in adirection vertical to the conveying direction A (FIG. 1), theperformance required for the hardware of the respective components iskept unchanged, and hence the cost of the system is not increased.

There can be provided a low-cost high-precision bill identifying andchecking apparatus 1 capable of detecting the outer contour of the bill6 with precision less than the pixel 40 which can be sensed by the linesensor 23.

As compared to reducing the interval of conveyance pulses for the linesensor 23 to read the bill 6, disposing the line sensor in the inclinedstate makes it possible to lower the specifications necessary for theimage data processing to a greater degree, there can be provided alow-cost bill identifying and checking apparatus 1 capable of executingprocessing at a higher speed.

Although the pixel 40 of the binary image B is configured as a rectanglehaving one and the same length in the conveying direction and theconveying width direction, the present invention is not restricted bythe configuration. The length of the pixel in the conveying directionmay differ from that in the conveying width direction. Also in thisconfiguration, the contour of the bill 6 can be appropriately obtained.

Although the optical line sensor 23 is inclined by an angle of θ withrespect to the conveying width direction, it is also possible toconfigure the apparatus in which the unit of the line sensor 23 isdisposed in parallel with the conveying width direction and the lightprojecting elements and the light receiver element array are inclined byan angle of θ with respect to the conveying width direction.

The present invention is not restricted by the configuration describedabove, but there can be considered many embodiments of the presentinvention.

According to the present invention, there can be provided a paper sheetidentifying and checking apparatus in which even if the inclination ofthe paper sheet with respect to the direction vertical to the conveyingdirection is almost zero, the paper sheet can be detected in theconveying direction with precision less than the period of conveyancepulses, without increasing the cost of the apparatus.

It should be further understood by those skilled in the art thatalthough the foregoing description has been made on embodiments of theinvention, the invention is not limited thereto and various changes andmodifications may be made without departing from the spirit of theinvention and the scope of the appended claims.

1. A paper sheet identifying and checking apparatus, comprising: aconveying path for conveying a paper sheet; a line sensor including aplurality of sensor elements arranged on the conveying path in a stringin a conveying width direction indicating a direction of width of theconveying path; and identifying means for identifying the paper sheet onthe basis of image data produced by the line sensor by reading the papersheet, wherein the direction of arranging the sensor elements isinclined with respect to the conveying width direction of the conveyingpath.
 2. A paper sheet identifying and checking apparatus according toclaim 1, wherein the angle of inclination of the sensor elements of theline sensor with respect to the conveying width direction is more than askew allowance angle allowed for the paper sheet to incline on theconveying path.
 3. A paper sheet identifying and checking apparatusaccording to claim 1, wherein the paper sheet includes a paper sheet ina shape of a rectangle, the apparatus further comprising: inclinationangle calculating means for calculating an inclination angle indicatingan angle of inclination of the paper sheet with respect to the conveyingwidth; and outer contour detecting means for detecting an outer contourof the paper sheet according to the inclination angle thus calculated.4. A paper sheet identifying and checking apparatus according to claim2, wherein the paper sheet includes a paper sheet in a shape of arectangle, the apparatus further comprising: inclination anglecalculating means for calculating an inclination angle indicating anangle of inclination of the paper sheet with respect to the conveyingwidth; and outer contour detecting means for detecting an outer contourof the paper sheet according to the inclination angle thus calculated.5. A paper sheet identifying and checking apparatus according to claim1, wherein the line sensor is disposed to cover almost entirely theconveying width of the conveying path.
 6. A paper sheet identifying andchecking apparatus according to claim 2, wherein the line sensor isdisposed to cover almost entirely the conveying width of the conveyingpath.
 7. A paper sheet identifying and checking apparatus according toclaim 3, wherein the line sensor is disposed to cover almost entirelythe conveying width of the conveying path.
 8. A paper sheet identifyingand checking apparatus according to claim 1, further comprising: arotary encoder for generating a pulse at a fixed period corresponding toa speed of conveying the paper sheet; a frame memory for obtaining imagedata from the line sensor at timing synchronized with the pulse andholding the image data therein; and image processing means forprocessing the image data held in the frame memory.
 9. A paper sheetidentifying and checking apparatus according to claim 2, furthercomprising: a rotary encoder for generating a pulse at a fixed periodcorresponding to a speed of conveying the paper sheet; a frame memoryfor obtaining image data from the line sensor at timing synchronizedwith the pulse and holding the image data therein; and image processingmeans for processing the image data held in the frame memory.
 10. Apaper sheet identifying and checking apparatus according to claim 3,further comprising: a rotary encoder for generating a pulse at a fixedperiod corresponding to a speed of conveying the paper sheet; a framememory for obtaining image data from the line sensor at timingsynchronized with the pulse and holding the image data therein; andimage processing means for processing the image data held in the framememory.
 11. A paper sheet identifying and checking apparatus accordingto claim 5, further comprising: a rotary encoder for generating a pulseat a fixed period corresponding to a speed of conveying the paper sheet;a frame memory for obtaining image data from the line sensor at timingsynchronized with the pulse and holding the image data therein; andimage processing means for processing the image data held in the framememory.